Figure 4. --The same area six growing sea- 

 sons after , planting [photo taken 

 October 1974) . 



Substantial differences occurred in average height growth between species at the end of 

 the sixth growing season. Bitterbrush, regardless of seed source, had better (P<0.05) height 

 growth than wedgeleaf ceanothus. There were no differences (P>0.05) in sixth-year heights 

 between the seeding and transplanting treatments of eitlier bitterbrush or ceanothus. 



Sixth-year survival and height of bitterbrush planted from local seed sources varied by 

 site (table 4). Survival was strongly related to topographic influences. Generally, the 

 higher survival rates were on lower and ui^per slo]ic positions. Tliis was true for both the 

 seeding and transplant treatments. Height growtli followed a similar pattern except for a 

 slower growth rate on the extreme up]")er slope position. Season-long soil moisture trends 

 measured during the first year were highest on the lower slope sites. 



Plants on slopes that were either liori zontal ly or vertically concave or convex had higher 

 survival. Those slope shapes were generally associated witli tlie uj^per and lower slope posi- 

 tions. Lower survival rates were found on vcrticall}' and lior i zontal ly straight mid-slopes. 

 Slope gradients under 65 percent and those with soutlieast aspects generally had better bitter- 

 brush survival tlian steeper slopes and those facing soutli or southwest. There are exceptions 

 to tlicse generalities and there is probably some confounding among the topographic variables. 



Each scalp on each of the 12 sample blocks was classified as to the nature (annual, 

 ]icrcnnial) of the proximate competing vegetation. There was a tendency toward lower bitter- 

 brush survival on those blocks liaving tlie largest percentage of scal]is with predominantly 

 perennial competing vegetation (fig. 5). Most of the perennial competition was from bluebunch 

 wheatgrass and arrowleaf balsamroot. Holmgren (1955) documented the competitive effect of cheat 

 grass and otlier annual vegetation on tlic survival of seedling bitterbrush. Our study was not 

 designed to direct 1\' evaluate the effects of plant comjiet it ion . Nevertheless, the data at least 

 suggest that pereimial vegetation may have a stronger competitive influence on bitterbrush 

 seedling survival than annual vegetation. Apparentl\", scalping effectively reduces competition 

 from annuals. But perennial plants near tlic jK^rimcter of the scalp may extend their roots 

 farther laterally and dejilete soil moisture througliout the growing season. 



Each time survival counts were made, we recorded the apj'iarent causes of mortality that had 

 occurred since the previous observation, rclx'ing heavil\- on personal judgment. Because survival 

 counts began on May 1, we probabl}' missed earl_\' post emergence mortality. 



Drought accounted for 50 percent of 5-year seedling mortality and 29 percent of 5-year 

 trans]Tlant mortality (table 5). Heat and frost lieaving caused minor mortality. 



Causes of Mortality 



8 



